Heretofore, yarn brake mechanisms positioned in an enlarged cavity of a yarn passageway in a hollow carrier mechanism of a spindle assembly of a textile yarn processing machine, particularly a two-for-one twister, have been proposed, such as shown in U.S. Pat. No. 3,490,221, issued Jan. 20, 1970, and assigned to the assignee of the present invention, and reference may be had to that patent for a disclosure of such prior yarn brake mechanisms. As may be seen in the aforementioned U.S. Pat. No. 3,490,221, this prior yarn brake mechanism included broadly a stationary, inclined, braking surface and a movable, pivotally mounted, braking plate for cooperation therewith and for receiving the yarn therebetween for applying a desired tension to the yarn as it passes through a hollow yarn carrier mechanism of a spindle assembly of the two-for-one twister textile yarn processing machine.
While this previously proposed yarn brake mechanism has been commercially effective for applying desired tensions to the yarn as it is being processed in the yarn processing machine, it required positive movement of the movable braking plate away from the stationary braking surface during threading of the yarn through the spindle assembly for start-up of the spindle assembly prior to yarn processing which was somewhat undesirable. Additionally, with the advent of automatic threading mechanisms for such spindle assemblies of textile yarn processing machines, such as, for example, disclosed in U.S. Pat. No. 3,731,478, issued May 8, 1973, and assigned to the assignee of the present invention, this requirement for positive movement of the movable braking plate away from the stationary braking surface, during threading of the yarn through the spindle assembly for start-up of the spindle assembly, has caused additional problems in the use of such automatic threading mechanisms.